The role of pH in the regulation of carbon fixation in the chloroplast stroma. Studies on CO2 fixation in the light and dark.
The role of pH in the regulation of carbon fixation in the chloroplast stroma. Studies on CO2 fixation in the light and dark.
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DOI：
10.1016/0005-2728(75)90041-9
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发表时间：
1975-08
期刊：
影响因子：
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通讯作者：
Karl Werdan;Hans W. Heldt;Mirjana Milovancev
中科院分区：
文献类型：
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作者：
Karl Werdan;Hans W. Heldt;Mirjana Milovancev
1.在20℃的黑暗和光照条件下，在一些叶绿体制剂中测量了基质和类囊体腔的pH，光照使类囊体腔的pH降低1.5，基质的pH增加近1个pH单位。二氧化碳的固定强烈依赖于基质中的pH。该酶的最适pH为8.1，在pH 7.3以下几乎为零。磷酸甘油酸还原是CO2固定的部分反应，对pH的依赖性很小。低浓度的解偶联剂-氯羰基氰基苯肼(CCCP)抑制了CO2的固定，而不影响磷酸甘油酸的还原。这种对二氧化碳固定的抑制似乎是由于CCCP.4逆转了光诱导的间质碱化。与CCCP相比，甲胺的作用非常不同。甲胺浓度的增加对二氧化碳固定和磷酸甘油酸还原的抑制程度相同。光诱导的基质碱化似乎不会被甲胺显著抑制，但类囊体腔中的质子被中和。高浓度甲胺对二氧化碳固定的抑制可以通过抑制光磷酸化来解释。看来，甲胺并不能消除质子的传输。研究表明，完整的叶绿体能够在黑暗中固定二氧化碳，产生3-磷酸甘油。这需要添加二羟丙酮磷酸盐作为核糖磷酸盐的前体，并提供三磷酸腺苷，并添加草酰乙酸酯用于基质中NADPH的再氧化。在磷酸二羟丙酮和草酰乙酸酯存在下，暗固定CO2与在光下固定CO2具有相同的pH依赖性。这表明，除非人工将介质中的pH值提高到8.8.7，否则不可能在黑暗中固定二氧化碳。结果表明，光照后基质中的pH变化足以使CO_2固定化从零切换到最大活性。这为光控制二氧化碳固定提供了一种机制，避免了在黑暗中浪费二氧化碳固定。
1. The pH in the stroma and in the thylakoid space has been measured in a number of chloroplast preparations in the dark and in the light at 20 °C. Illumination causes a decrease of the pH in the thylakoid space by 1.5 and an increase of the pH in the stroma by almost 1 pH unit.2. CO2fixation is shown to be strongly dependent on the pH in the stroma. The pH optimum was 8.1, with almost zero activity below pH 7.3. Phosphoglycerate reduction, which is a partial reaction of CO2fixation, shows very little pH dependency.3. Low concentrations of the uncouplerm-chlorocarbonylcyanide phenylhydrazone (CCCP) inhibit CO2fixation without affecting phosophoglycerate reduction. This inhibition of CO2fixation appears to be caused by reversal of light induced alkalisation in the stroma by CCCP.4. Methylamine has a very different effect compared to CCCP. Increasing concentrations of methylamine inhibit CO2fixation and phosphoglycerate reduction to the same extent. The light induced alkalisation of the stroma appears not to be significantly inhibited by methylamine, but the protons in the thylakoid space are neutralized. The inhibition of CO2fixation by higher concentrations of methylamine is explained by an inhibition of photophosphorylation. It appears that methylamine does not abolish proton transport.5. It is shown that intact chloroplasts are able to fix CO2in the dark, yielding 3-phosphoglycerate. This requires the addition of dihydroxyacetone phosphate as precursor of ribulosemonophosphate and also to supply ATP, and the addition of oxaloacetate for reoxidation of the NADPH in the stroma.6. Dark CO2fixation in the presence of dihydroxyacetone phosphate and oxaloacetate has the same pH dependency as CO2fixation in the light. This demonstrates that CO2fixation in the dark is not possible, unless the pH in the medium is artificially raised to pH 8.8.7. It is shown that pH changes occurring in the stroma after illumination are sufficient to switch CO2fixation from zero to maximal activity. This offers a mechanism for light control of CO2fixation, avoiding wasteful CO2fixation in the dark.